bump up version to 1.7.1

add testing framework architecture diagram

bump up version to 1.6.2

bump up version to 1.6.1

fix make lint

fix mini-wallet app: validate payment command with prior payment comm…

…and (#280)

1. Validate payment command with prior payment command was accidentally removed during a refactoring, add the validation back.
2. Added tests for validating with prior payment:
    1. sender.kyc_data can only be written once.
    2. sender.address can only be written once.

bump up version to 1.5.2

fix doc typo

bump up version to 1.5.0 for new release

bump up to version 1.4.0

bump up version for the next release